Conventionally, the production of extruded products, including coverings such as insulation and jacketing about wires and cables, from compositions based on water-curable, silane modified polymers has been carried out by feeding a composition containing a silane, a thermoplastic polymer and a catalyst to a single extruder wherein the components are blended and reacted to effect a grafting of the silane onto the polymer and from whence the composition containing the water-curable, silane modified polymer is extruded as a shaped product.
It has been found, however, that the production of extruded products from a single, conventional extruder requires the exclusion of moisture from the materials fed to the extruder and careful control of operating parameters, in general, in order to avoid the formation of voids in the extruded products.
The problem of voids in the extruded products has led to a modification of the single extruder approach of grafting a silane onto a thermplastic polymer and of extruding the resultant water-curable, silane modified polymer into a shaped product. As an alternative, it has been proposed to use a plurality of extruders, as disclosed in U.S. Pat. No. 4,136,132, patented Jan. 23, 1979. This expedient, however, has not substantially eliminated the formation of voids in the extruded products.